Parental Income Alters Development of Anterior, but not Posterior, Hippocampus

• In Event: 1-218 - How the Environment Shapes Learning Across Development

Integrative Statement

Low childhood socioeconomic status (SES) is associated with worse cognitive performance, including poorer episodic memory and vocabulary (Hackman & Farah, 2009; Farah, 2017). These cognitive disparities are thought to be driven, at least in part, by the impact of income-related stress on the developing brain (Sheridan & McLaughlin, 2014). The volume of the hippocampus, a key region for memory, is consistently positively correlated with SES (Farah, 2017), and in animals, is highly sensitive to neurochemical responses to stress (Sapolsky, Krey, & McEwen, 1985). Despite these findings, few studies have shown that hippocampal volume mediates relations between SES and memory development. Critically, this may be because prior studies examine the hippocampus as a single, unitary structure; however, the hippocampus is comprised of distinct anterior and posterior subregions, which display unique developmental trajectories (Gogtay et al., 2006), associations with cognition (Poppenk & Moscovitch, 2011), and vulnerabilities to chronic stress (Szeszko et al., 2006). Animal models suggest that anterior hippocampus may be particularly susceptible to chronic stress because of its role in regulating the hypothalamic-pituitary-adrenal (HPA) stress response. Damage to this region in animals increases the stress response (Herman, Dolgas, & Carlson, 1998), which may render the hippocampus more vulnerable to stress-induced insults. In light of this research, our study aimed to (1) investigate whether SES had larger influences on anterior than posterior hippocampal development; (2) assess whether regional effects within the hippocampus mediate links between SES and cognition.

We investigated these questions using a large sample of healthy children and adolescents (N = 703, mean age = 12.16, range = 3-21), recruited through the Pediatric Imaging, Neurocognition, and Genetics study (Jernigan et al., 2016). To estimate socioeconomic status, we used annual household income, reported by participants’ parents (range = <$5,000 - >$350,000). Each participant also underwent structural MRI scanning, and completed episodic and vocabulary assessments. In order to measure hippocampal volumes, we used the Multiple Automatically Generated Templates algorithm to label the hippocampus (Chakravarty et al., 2013). A trained researcher further delineated the hippocampus into subregions, using the uncal apex as a landmark for the anterior-posterior boundary.

We observed a significant positive effect of income on anterior hippocampal volumes ( = 0.0004, p < .001). In contrast, there was no effect of income on posterior hippocampus ( = −0.0002, p = .19). A significant interaction between subregion and income ( = −29.56, p < .001) revealed that income selectively influenced the anterior hippocampus. Critically, anterior, but not posterior hippocampal volumes partially mediated relations between SES and both episodic memory (p = 0.02) and vocabulary (p = 0.008).

Our findings indicate that the anterior hippocampus is selectively vulnerable to low SES. Critically, altered anterior hippocampal development may impair regulation of the stress response, rendering the hippocampus vulnerable to stress-induced neurotoxicity. Moreover, the anterior hippocampus may play a mechanistic role in mediating SES-related discrepancies in cognition. Given research showing hippocampal subregions are associated with distinct memory processes, future studies should aim to understand whether different cognitive profiles are associated with variations in SES.

Authors

• Alexandra Lee Decker, The University of Toronto
  Presenting Author

• Katherine D. Duncan, University of Toronto
  Non-Presenting Author

• Amy S Finn, University of Toronto
  Non-Presenting Author

• Donald Mabbott, University of Toronto
  Non-Presenting Author